Prior art proposals for laser removal of unwanted deposits or diseased tissue from inner wall linings of a blood vessel are known. These techniques are generically referred to as percutaneous transluminal laser angioplasty (PTLA). The use of laser catheters for treatment of carotid and coronary artery stenoses have been proposed and preliminary tests that have been conducted suggest these devices can effectively increase blood flow through partially or totally blocked blood vessels.
A printed publication to Cothren, et al. entitled "A Multi Fiber Catheter with an Optical Shield for Laser Angiosurgery," Lasers in the Life Sciences 1(1), 1986,
1-12, documents a proposed catheter system having multiple optical fibers. The optical fibers extend the length of a laser catheter and direct light at the catheter's distal end through an optical shield. The system proposed in this publication includes 19 optical fibers arranged to include a center fiber, an inner ring of 6 fibers, and an outer ring of 12 fibers. The excitation or firing sequence of the fibers is controlled by a computer. The goal of each firing sequence is to produce a hole within diseased arterial tissue. The firing sequence is conducted and the laser catheter tip can be inserted further into the hole before a next firing sequence conducted.
The article to Lammer, et al. entitled "Contact Probes for Intravascular Laser Recanalization" in Radiology, 1989, 24. discloses a laser catheter having a single optical light pipe which terminates at a distal end of the catheter and is covered by a sapphire tip which concentrates or focuses the excitation light delivered through the fiber optic light pipe to a focused region in close proximity to the sapphire tip. Some light scattering occurs at the entry and exit boundaries of the sapphire tip so that as noted in this publication "circumferential energy distribution also occurs."
U.S. Pat. No. 4,854,315 to Stack, et al. concerns a laser catheter having multiple light pipes which extend through a catheter body to deliver light energy to the distal tip of the catheter. The multiple light pipes are spaced around a center axis of the catheter and terminate in proximity to a window which conducts the light from the multiple light pipes to the vessel being treated.